1. Field of the Invention
The invention relates in general to a light guide device, and more particularly to a light guide device for increasing light utilization rate and a light guide plate using the same.
2. Description of the Related Art
Please referring to FIG. 1, part of a conventional backlight module is illustrated. The backlight module 100, such as a side-light type backlight module, includes a light source 110 and a light guide plate 120. The light guide plate 120 is generally a wedge plate or a flat plate and has a light incident surface R1 and a light emitting surface R2. The light source 110, such as a light emitting diode (LED) light bar, is disposed near the light incident surface R1 for generating light. The light enters the light guide plate 120 through the light incident surface R1. Then, the light is emitted out from the light guide plate 120 through the light emitting surface R2 and becomes a surface light source. Furthermore, several optical sheets (not shown in drawings) are disposed between the light guide plate 120 and a display panel (not shown in drawings) for uniformizing the light from the light emitting surface R2 and increasing the luminance. As a result, the backlight module for the display panel is improved.
However, when the thickness of the light guide plate 120 is reduced, the light generated by the light source 110 can not effectively enter the light guide plate 120, which means that the light received by the light incident surface R1 is decreased. Therefore, the thickness of the light guide plate 120 can not be reduced randomly. Generally speaking, the light incident surface R1 has to be corresponding to the field that the light projected onto, as shown in FIG. 1. Furthermore, when the light source 110 is a LED light bar, several packages with LED chips are arranged at the same intervals on the light bar. Each package has a light emitting range of 120° substantially. As a result, the space near the light bar and between two adjacent packages is dark. Accordingly, the area (the dotted area in FIG. 1) of the light emitting surface R2 adjacent to the light incident surface R1 becomes relatively dark. In other words, the surface light source emitted from the light emitting surface R2 is non-uniform. In order to solve this problem, the distance between the light source 110 and the light incident surface R1 is increased. However, the luminance of the light emitting surface R2 is lowered, and the arrangement of other components, such as a plastic frame or a lamp holder, is limited. Besides, the light received by the light incident surface R1 is reduced because light leakage occurs on a side of the non light-emitting region of the package.
Therefore, it is very important to solve the above problems for reducing the volume of the display and increasing the light utilization rate.